Magnesium alloys



Unite MAGNESIUM ALLOYS No Drawing. Application May 26, 1954 Serial No. 432,576

Claims priority, application France November 9, 1953 2 Claims. (Cl. 75-468) Alloys of the group magnesium zinc or magnesiumzinc-manganese are already well known in which cerium is incorporated, either in the pure state or in the form of mischmetall (rare earths) so as to make them less subject to micro-porosity. The alloys obtained in this Way are, however, extremely difficult to prepare; they are indeed very oxidisable, very inclined to form a coarse crystallisation, and finally they are very sensitive to the proportion of the silicon content of the alloy. On the other hand, the problem of micro-porosity cannot be resolved for these alloys other than by a compromise, since a choice must be made between very good mechanical characteristics accompanied by micro-porosity (having a high zinc content and a low content of mischmetall), or on the other hand, an absence of microporosity which is accompanied by low mechanical characteristics (a low zinc content and a high content of mischmetall) The applicants decided to obtain alloys which, as far as possible, were free from all these various drawbacks. To this end, they studied in a systematic manner the specific effect on these alloys of the main rare earths applied to them one by one, while at the same time taking advantage of the known useful properties obtained by the presence of beryllium, that is to say in contributing, to a large extent, to the avoidance of the detrimental effects of oxidation while hot.

In these circumstances, the applicants have found that among the rare earths which are usable on an industrial scale, lanthanum in the practically pure state (which means that it is present in a proportion of more than 90% in a rare earth) gives the most favourable results in avoiding or reducing micro-porosity.

In accordance with the present invention, use is made of practically pure lanthanum in a content which is preferably of the order to 0.5 to 1.5%. It has been found in particular that a 6% zinc alloy containing lanthanum is practically free from micro-porosity.

A particular alloy of magnesium which conforms with the invention has the following composition:

Zinc 6 to 7%.

Lanthanum, practically pure--. 0.5 to 1.5%, for preference.

Aluminium 0.5% for preference.

Beryllium 0.01%.

Silicon Admissible up to 0.15%.

Magnesium The remainder.

2,839,394 Patented June 17, 1958 The addition of didymium made in accordance with these conditions to the alloys magnesium-zincaluminium (0.5%)-beryllium (0.01%), enables high mechanical characteristics to be obtained, even in cases where the zinc content is low and the didymium content is high, for example 1.5%.

A particular alloy which has these characteristics may have the following composition:

Zinc 5 to 7%.

Didymium 0.5 to 2%.

Aluminium 0.5% for preference. Beryllium 0.01%.

Silicon Admissible up to 0.15%. Magnesium The remainder.

It will be observed that the presence of silicon may be admitted in the alloys according to the invention up to a limiting content which is about ten times greater than the safe limit which could have been permitted in the case of previous alloys, if acceptable mechanical characteristics were to be obtained.

Finally, it will be seen that the advantageous results accruing from the use of didymium enable the elimination of the usual dilemma, referred to at the beginning of this specification, in the case of the group of alloys magnesium-zinc-mischmetall.

The invention especially includes alloys which conform to these characteristics and in which the didymium used with a preferred content of 0.5 to 2% has the following composition:

Percent Neodymium 60 to Praseodymium 10 to 15 Samarium 16 to 17 Lanthanum 0. to 10 Cerium 0 The invention also comprises a heat treatment applied to the alloys which have the characteristics referred to above.

Homogenisation is carried out in two temperature stages, the first at about 338 C. and. the second at a temperature in the vicinity of 460 C. By this means, increase of grain size during heat treatment is avoided. For hardening, simple cooling in air is suflicient. This homogenising treatment is followed by a tempering process which is also carried out in two temperature stages, for example, the first stage at 140 C. and the second at 160 C. These tempering temperatures can, however, be varied between fairly wide limits; for the first stage between and 150 C., and for the second stage between and 200 C. depending onthe results it is desired to obtain and the composition of the alloy.

What we claim is:

1. Magnesium alloys of the group comprising magnesium, zinc, aluminium, glucinum, the said alloys having the following composition:

Zinc 6 to 7%. Lanthanum, practically pure 0.5 to 1.5%. Aluminium About 0.5%. Beryllium About 0.01%. Silicon a Up to 0.15% max.

Magnesium The remainder.

3 4 2." Magnesium"alloye'as'claimedinclaim'1"iii whieh" 25492955 JesSup et'al. Apr. 24, 1951 the said lanthanum is utilized in the form of rare earths, 2,569,477 Leontis Oct. 2, 1951 containing up te substantially 4% neodymium and up, to 2,609,309 Meier Sept. 2, 1952 substantially"4%" prasebdymium, the reinaindef being 2,622,049 Hesse Dec. 16, 1952 lanthanum. 5 I

I y x FOREIGN PATENTS References Cited m the tile oi tins patent 113,802, Austria Sept 18; 1941 UNITED STATES PATENTS 693,478 Great Britain July 1, 1953 1,941,039 Luschenowsky Dec. 26, 1933 2,302,968 McDonald Nov; 24, 1942 10 OTHER REFERENCES 2,420,293 Bedk-et-al. May 13, 1947 Journal of Metals, v01. 1, pp. 968-983, December 1949. 

1. THE METHOD FOR IMPROVING MOLTEN CAST IRON WHICH SIUM, ZINC, ALUMINIUM, GLUCINUM, THE SAID ALLOYS HAVING THE FOLLOWING COMPOSITION: 